Five of the largest U.S. banks have provided $19 billion in mortgage debt write-downs to some 240,000 borrowers under the terms of a federal and state settlement of foreclosure-processing violations reached one year ago, according to a watchdog's report released Thursday.

Bank of America Corp., which was required to provide the majority of relief under the foreclosure pact, has accounted for the lion's share of principal write-downs, with about $13.5 billion in homeowner debts written off. The Charlotte, N.C., lender...